Working in physics: Life on the borders

Edward Barry describes a career at the sharp end of interdisciplinary research, and how a virus from the New York City sewers is helping shape our understanding of nanoscale self-assembly.

Interdisciplinary science has been a hot topic for more than a decade, with increasing numbers of researchers working on projects that do not fit into neat departmental boxes like "physics" or "biology". Yet despite this increased activity, the structures in place to support these interdisciplinary scientists – including research grants and training for PhD students – have sometimes lagged behind. One programme that aims to help fill this gap for students of biomedical, physical and computational sciences is the Interfaces Initiative, a joint project of the Howard Hughes Medical Institute and the US National Institute of Biomedical Imaging and Bioengineering. Physics World talked to a current Interfaces participant, Edward Barry, who is finishing his PhD in biology-related condensed-matter physics at Brandeis University in Massachusetts.

What attracted you to biophysics?I became interested in biophysics-motivated research while working as a research assistant in Zvonimir Dogic's complex-fluids group at the Rowland Institute at Harvard University. I got plenty of hands-on experience in all of the projects the lab was working on, as well as other research at the institute. This was a great learning experience in general, and during invited talks at the institute and through collaborations with visiting scientists and researches in the Cambridge area, my interest in biological systems solidified. This interest carried on when we moved the lab to Brandeis University, where I began my PhD studies.

What does your research involve?We study physics using various biological systems, including one particular virus, called the fd virus, that was originally discovered in the New York City sewer systems. The fd virus has a long, thin shape, making it ideal for studying hard, rod-like particles that repel each other. Indeed, such "filamentous" viruses have a long history of being used for this purpose. For example, experiments with the tobacco mosaic virus (TMV) inspired the chemical physicist Lars Onsager to present his seminal theory describing the way in which suspensions of rod-like molecules can go from being randomly oriented to adopting a more ordered state in which the long axes of the rods, on average, align along a particular direction. Onsager's work on this isotropic-nematic liquid-crystalline phase transition laid the foundation for our understanding of liquid crystals, which are now common in the displays for TVs, computer screens and other electronic devices.

In our fd system, we can obtain large quantities of identical particles (1016) in a matter of days – a significant advantage over the TMV system, which takes months to grow. In our system, we simply grow litres of bacteria, infect them with the virus, and the next day we have enough of the virus to do experiments for weeks.

Due to the collective efforts of researchers over the past 20 years, the behaviour of suspensions of the fd virus has now been characterized in detail. These 880 nm long rod-like particles interact in suspension through hard-core repulsive interactions and undergo a phase transition into a "twisted" nematic phase as their concentration in the suspension increases. This transition is only qualitatively described in the original Onsager theory, as the viruses are not quite rigid rods but have a certain finite flexibility. However, we have been able to demonstrate that a mutant virus, known as fdY21M, is four times as rigid as the wild-type virus, and in 2009 we published a paper where we showed that its phase transition is described quantitatively by the original Onsager theory (see Soft Matter5 2563).

What else can you do with these biological systems?By adding a non-adsorbing polymer to suspensions of these rod-like particles we can also change the interaction potential between rods, thus allowing us to see how hard rods behave in the presence of some degree of attraction. The polymer introduces an attractive interaction between the rods via the depletion interaction. This occurs when the distance between the rods becomes less than the size of the polymer, such that the polymer can no longer fit between them.

When this happens, an imbalance in os_motic pressure forces the rods even closer together. When we studied this process, we were surprised to observe the formation of fluid-like 2D surfaces, known as monolayer membranes. These membranes have properties identical to those of lipid bilayers, which are the main constituents of the flat sheets that form a barrier around almost all living cells. In our system, the membranes can be quite large (hundreds of microns in diameter) and their existence seems to suggest a new unexplored and easily scalable mechanism for the self-assembly of 2D materials.

Another system we have used in our research uses bacterial flagella – the helical filaments that act as the rotor for bacterial movement. After removing the cell bodies, we can isolate these helical particles and create suspensions of pure helical rods. We have shown that these particles also undergo a concentration-dependent, first-order phase transition into a chiral, or "handed", liquid-crystalline state called the conical phase. These liquid crystals have interesting bulk chiral properties that are determined by the chirality of their constituent particles.

What are some of the challenges of doing interdisciplinary research?One of the biggest hurdles stems from the different language that researchers use. It may seem trivial, but differences in scientific language, and understanding what different scientific terms mean and imply, is really important. This is most apparent at conferences or when attending scientific talks. On many occasions, a failure to understand certain biological terms and concepts has left me utterly and completely lost five minutes into a talk that might otherwise have been very interesting and informative.

How has support and training from the Interfaces Initiative helped you?Above all else, it has enabled me to become more versed in the methods of biological research. With unique opportunities, both inside and outside of the classroom, this aspect of the programme, which is designed to educate and train, has been by far the greatest assistance I have received. For example, I recently won the Interfaces Scholar Award, which means I get to deliver three hour-long lectures to members of the quantitative-biology programme at Brandeis. Preparing lectures that are engaging and useful for postgraduate students, postdocs and professors working in different fields has certainly been a challenge, but opportunities like this really help strengthen the multidisciplinary dialogue.

What advice do you have for physics students interested in biology-related problems?One of the most important things a physics undergraduate student or a recent graduate can do is get involved in research. Whether it is in a theory group or in the lab, many biological researchers can benefit from physicists' input and training. Designing optical tweezers, introducing improved methods in microscopy, or even programming simulations – these are just a few examples of the many opportunities for physicists and recent physics graduates.

Talk to researchers who are doing something that you find interesting. You can send them an e-mail or go and speak to them at a conference if they sparked your interest. One key thing to remember, though, is that in the end, no-one is going to come looking for you just because you have a degree in physics. However, your training as a physicist means you can offer different skills to someone with a degree in biology or chemistry, so use this to your advantage.

What do you plan to do next?I expect to finish my PhD in the very near future, and I have begun looking for postdoc opportunities. I have always wanted to teach undergraduates and postgraduates while also conducting research in a university setting. However, I am also considering positions in industry. With a degree in quantitative biology and research experience at the interface between biological and physical science, I hope to find a position that is not restricted to purely physical science, such as working on solar energy or the design of photovoltaic systems.

About the authorEdward Barry is a PhD student at Brandeis University, US, email edb@brandeis.edu

This article originally appeared in the February 2010 issue of Physics World